Peripheral Nervous System

Question 1

Types of axonal injury in PNS

Answer 1

Wallerian degeneration
Axonal degeneration
Segmental demyelination

Question 2

Wallerian degeneration

Answer 2

Transaction of axons (by trauma or compression) —> loss of distal segment, axon/myelin at injury site, proximal segment of injury next to node —> axonal flow halted —> accumulation of neuro filaments, mitochondria, debris —> swelling of degenerated axon (spheroid) —> distal segment Wallerian degeneration (removed by macrophages) —> axonal sprouting/segmental remyelination—> NMJ reestab.

Central chromatolysis also observed, but reversible

Question 3

Factors affecting success of Wallerian degeneration

Answer 3

Endometrium must be intact

How distal is the lesion? How far apart are the severed ends of nerve? How much damage/debris sis around injury site

Question 4

Neuroma

Answer 4

Result of unsuccessful PNS regeneration
Small painful nodule of axons/Schwann cells

Dysfunction of healing (not neoplasm)

Question 5

Axonal degeneration

Answer 5

Occurs due to metabolic derangement of neuron —> death of distal portion of axon (lose both myelin and axon)

Can look similar to Wallerian, but different cause (inherited, metabolic, toxic, and diseases)

Regeneration poor

Question 6

Polyneuritis equi

Answer 6

(Aka Cauda Equina syndrome)

Progressive inflammation of caudal spinal cord / nerve trunk so of cauda equine of horses - unknown cause (immune mediated?)

Clincial signs: ataxia, pain, dropped tail, urinary incontinece, fecal retention, muscle loss

Nerve roots thickened, fusiform, yellow discoloration; granulomatous inflammation/fibrosis

Question 7

Histology of polyneuritis

Answer 7

Nodular aggregates of granulomatous inflammation around nerves

Characterized by macrophages

Expansion of perineurium/epineurium by fibrosis

Question 8

Acquired myasthenia gravis

Answer 8

Auto-antibodies to acetyl choline receptor block function

Responds to anti-acetylcholinesterase therapy

Can be self-limiting

Question 9

Congenital myasthenia gravis

Answer 9

Deficiency of acetyl choline receptors (no circulating antibodies to ACh receptors)

Responsive to anti-cholinesterase therapy - reduced cholinesterase —> increased available ACh at synapse

Jack Russel terriers, springer spaniels, smooth haired fox terriers

Question 10

Infectious causes of NMJ disorders

Answer 10

Botulism
Tetanus

Question 11

Botulism

Answer 11

Botulinum toxin from C. Botulinum blocks release of acetylcholine

Generalized FLACCID paralysis

Question 12

Tetanus

Answer 12

Tetanospasmin toxin from C. Tetani —> binds inhibitory interneurons —> blocks release of inhibitory neurotransmitter

SPASTIC/rigid paralysis

Question 13

Equine laryngeal hemiplegia

Answer 13

Progressive (Wallerian) degeneration of axons of left recurrent laryngeal nerve

Denervation atrophy of cricoarytenoideus dorsalis muscle of left side of larynx

Causes: trauma to nerves, extension of inflammation from guttural pouch

Question 14

Brachial plexus avulsion

Answer 14

Acute exacerbated abduction of forelimb/stretching of brachial plexus nerves

Causes: jumping from high place

Recovery depends on severity of stretching/fibrosis

Question 15

Equine peripheral neuropathy

Answer 15

Uncommon

Injury to nerve/nerve roots of brachial plexus (trauma, poorly fitted harness collar)

Question 16

Neoplasia of PNS

Answer 16

(Peripheral) nerve sheath tumors (from Schwann cells, peri neural cells, fibroblasts)

No widely accepted grading scheme to distinguish benign/malignant